The objective of our research is to define antigenic determinants of nicotinic acetylcholine receptors (AChR) relevant to the pathogenesis of an autoimmune disease of skeletal muscle, myasthenia gravis (MG) and to isolate determinants capable of suppressing the disease process in experimental autoimmune myasthenia gravis (EAMG). We will develop new serological techniques to define antigenic determinants of AChR, specifically those that are exposed extracellularly on muscle. Antigenicity of muscle AChR derived from thymus and selected skeletal sources will be compared serologically. Monoclonal antibodies produced by immune rat lymphocytes hybridized with mouse myeloma cells will be employed to purify solubilized AChR and also to isolate antigenic fragments released by controlled proteolytic digestion of AChR. Digestion with selected enzymes in mild conditions is aimed at preserving conformational antigenic determinants. Antibody products of B-lymphocytes from MG patients fused with a suitable myeloma line should give direct information about determinants of AChR involved in the pathogenesis of MG.